1. Field of the Invention
This invention relates to a method, device, and information signal recording medium for duplication control, for example, in which a video signal recorded in a recording medium is played back, the played back video signal is transmitted with information for preventing duplication together, the transmitted information signal is received to control or inhibit the recording of the information signal in another recording medium.
2. Description of Related Art
VTR (Video Tape recording devices) has been popularized in daily life, and many kinds of software which can be played back on a VTR are supplied abundantly. Digital VTR or DVD (Digital Video Disks) playback devices have been available commercially, and provide images and sound of exceptionally high quality.
On the other hand, there is, however, a problem in that this great abundance of software can be copied without restriction, and several methods have already been proposed to inhibit duplication.
For example, though the method is a method which inhibits duplication of an analog video signal not directly, one method to prevent copying uses a difference in the AGC (Automatic Gain Control) system, or in the APC (Automatic Phase Control) system, for example, between the VTR recording device and a monitor receiver for displaying the image.
For example, the method which utilizes the difference in AGC system, in which a VTR performs AGC using a pseudo sync signal inserted in the video signal and a monitor receiver employs a different AGC system not using the pseudo sync signal, is an example of the former, in detail, when an analog video signal is recorded in an original recording medium. A very high level pseudo sync signal is previously inserted as a sync signal for AGC, and the very high level pseudo sync signal is inserted in the video signal to be supplied from a playback VTR to a recording VTR as a sync signal for AGC.
VTR performs APC using the phase of the color burst signal itself in the video signal and the monitor receiver employs a different APC. The method which utilizes the difference in APC is an example of the latter, in detail, the phase of the color burst signal of a video signal is previously inverted partially when the analog video signal is recorded in an original recording medium, and the color burst signal having partially inverted phase is outputted as a video signal to be supplied from a playback VTR to a recording VTR.
As the result, the monitor receiver which receives the analog video signal from the playback VTR plays back the image correctly without being affected by the pseudo sync signal in AGC or without desired affection of the partial phase inversion of the color burst signal used for APC.
On the other hand, in a VTR, which is supplied with the analog video signal from the playback VTR into which pseudo sync signals have been inserted or which has been subjected to color burst signal phase inversion control as described herein above, for receiving such analog video signal and for recording the analog video signal in a recording medium, proper gain control or phase control based on the input signal cannot be performed, and so the video signal is not correctly recorded. Even if this signal is played back, therefore, normal picture and sound cannot be obtained.
As described herein above, in the case that involves an analog video signal, the prevention is not a method for directly inhibiting duplication but is a method for viewing an abnormally played back picture which can not viewed normally. Such prevention method is a passive duplication prevention control.
On the other hand, in the case that digitized information, for example, video signal is involved, an anti-duplication signal or an anti-duplication control signal comprising, for example, a duplication ranking control code, is added as digital data to the video signal and recorded on the recording medium, so as to prevent or control duplication of the image.
FIG. 1 is a basic structural diagram of a duplication apparatus for duplicating digitized information, a digital information played back by the digital playback device 110 is sent to a digital recording device 120 through a digital transmission line 101, and the digital recording device 101 duplicates the digital information if duplication is permitted and does not duplicate the digital information if duplication is not permitted.
An anti-duplication control information in the form of additional information is recorded in a recording medium 111 placed on the digital playback device 110 in addition to a digital main information. The anti-duplication control information indicates control content such as duplication inhibition, duplication permission, or generation restriction. The digital playback section 113 reads out the information from the recording medium 111, acquires the anti-duplication control information together with the digital main information, and sends them to the digital recording medium 120 through the digital transmission line 101.
An anti-duplication control signal detection section 122 of the digital recording device 120 detects the anti-duplication control signal out of the information items received from the digital transmission line 101, and judges the control content. The decision result is sent to a digital recording section 121.
If the decision result of the anti-duplication control signal from the anti-duplication control signal detection section 122 indicates permission of recording of the digital information inputted through the digital transmission line 101, then the digital recording section 121 converts the input digital signal to a digital information suitable for recording, and writes it in the recording medium 123, that is, recording is performed. On the other hand; if the decision result of the anti-duplication control signal from the anti-duplication control signal detection section 122 indicates duplication inhibition, then the digital recording section 121 does not perform recording processing of the input digital information.
Further, if the decision result of the anti-duplication control signal from the anti-duplication control signal detection section 122 indicates permission of recording of only the first generation, then the digital recording section 121 converts the input digital signal to a digital information suitable for recording, and writes it in the recording medium 123, that is, recording is performed, and additionally, converts the anti-duplication control signal in the form of additional information to a signal for indicating duplication inhibition (duplication inhibition of next generation), and records it in the recording medium 123. Therefore, the video signal can not be duplicated further using the recording medium 123 in which the information is recorded.
As described herein above, in the case of digital connection that the main information signal and anti-duplication control signal added as an additional information are supplied to a recording device in the form of digital signal, because the anti-duplication control signal is contained in the digital data to be transmitted, duplication prevention control such as duplication inhibition is performed consistently in a recording device using the anti-duplication control signal.
In the case that the digital playback device in FIG. 1 is, for example, a digital VTR, to monitor the played back video signal and audio signal, only both the video signal, that is the main information signal, and audio signal are converted to an analog signal through a D/A conversion circuit 113 and guided to an analog output terminal 114 connected usually to a monitor receiver.
As described herein above, though the playback device is a device for playing back digital signals, the anti-duplication control signal is not contained in the analog signal guided to the analog output terminal 114. Therefore, in the case of analog connection in which an analog device such as analog VTR is connected to the analog output terminal 114, duplication of the main information signal is undesirably possible.
Though it is considered that the anti-duplication control signal is superimposed and added on the D/A converted video signal and audio signal, it is difficult that the anti-duplication control signal is added, extracted in a recording device, and used in duplication prevention control without deterioration of the D/A converted video signal and audio signal.
Therefore, heretofore in the case of analog connection, only the passive duplication prevention method utilizing the difference in AGC system or the difference in APC characteristics between a VTR and monitor receiver described herein above has been an available duplication prevention control method.
However, in the case of the duplication prevention control method utilizing the difference in AGC system or APC characteristics between a VTR and monitor receiver described herein above, it is possible to record the video signal normally even with the passive duplication prevention depending on the AGC system or APC characteristics of recording device side. Further, disturbance of the played back picture on the monitor receiver can be caused. These are problems in duplication prevention control.
The inventors of the present invention have proposed previously a method in which a anti-duplication control signal is spectrally spread, the spectrally spread anti-duplication control signal is superimposed on the analog video signal, and the video signal is recorded in the form of digital record or analog record (refer to U.S. patent application Ser. No. 08/75510) as a duplication prevention control method which can solve the problem described herein above and is effective for both analog connection and digital connection without deterioration of the played back picture and sound.
According to this method, a PN (Pseudorandom Noise) sequence code (referred to hereinafter as PN code) used as a spread code is generated with a sufficiently short period and spectrally spread by multiplying it by the anti-duplication control signal. In this way, a narrow-band high-level anti-duplication control signal is converted to a wide-band low-level signal which does not affect the video signal or sound signal. This spectrally spread anti-duplication control signal is then superimposed on the analog video signal, and recorded in a recording medium. In this case, the signal to be recorded in a recording medium may be an analog signal or a digital signal.
In this method, because the anti-duplication control signal is spectrally spread and superimposed on the video signal as a wide-band low-level signal, it is therefore difficult for a person who wishes to illegally duplicate the video signal to remove the anti-duplication control signal which is superimposed on it.
However, it is possible to detect and use the superimposed anti-duplication control signal by performing inversion spectral spread. This anti-duplication control signal is therefore supplied to the recording device together with the video signal. In the recording side, the anti-duplication control signal is detected, and duplication is consistently controlled according to the detected anti-duplication control signal.
In the case that generation restriction such as permission of the first generation duplication or permission of two generation duplication is performed as described herein above using this method, a plurality of different spectrally spread anti-duplication control signal can be superimposed on the same time interval of, the video signal.
For example, in the case that the anti-duplication control signal added on the first generation recording medium is an information which indicates permission of only the first generation duplication, when duplication is performed using the first generation recording medium, the anti-duplication control signal which permits only the first generation duplication is spectrally spread and superimposed on the video signal recorded in the second generation recording medium.
When duplication is performed using the second generation recording medium, in addition to the information which permits only the first generation duplication, the information (information which indicates duplication inhibition) which indicates that the video signal recorded in the second generation recording medium can not be duplicated using this second generation recording medium is spectrally spread and superimposed on the video signal.
In the case that a plurality of different spectrally spread anti-duplication control signals are superimposed on the same time interval of the video signal, it is troublesome to extract only the newest anti-duplication control signal. For example, it is required that all the plurality of anti-duplication control signals superimposed on the same time interval of the video signal is extracted and which anti-duplication control signal is the newest anti-duplication control signal is judged. Therefore it takes a significant time and work to extract the newest anti-duplication control signal.
To cope with this problem, it is considered that a cancel signal having the same level and same phase as those of the old anti-duplication control signal superimposed previously which is spectrally spread and superimposed on the video signal is generated, and by subtracting this cancel signal from the video signal on which the spectrally spread anti-duplication control signal is superimposed, the spectrally spread old anti-duplication control signal superimposed on the video signal is canceled, thereafter a new spectrally spread anti-duplication control signal is generated and superimposed on the video signal.
If the old anti-duplication control signal spectrally spread and superimposed previously on the video signal is canceled as described herein above and only one anti-duplication control signal spectrally spread and superimposed on the video signal is always involved, then the anti-duplication control signal spectrally spread and superimposed on the video signal is extracted easily. However, it is required to cancel the old anti-duplication control signal, and it take significant time and work cancel the old anti-duplication control signal, Therefore this method is also not preferable.
As described hereinbefore, in the case of transmission of analog video signals, generation restriction on the analog video signal for restricting the number of duplications requires significant time and work, and the restriction is not performed rapidly and not correctly.
In view of the above, it is the object of the present invention to provides a method, device, and information signal recording medium which are capable of performing duplication prevention control of the information signal including restriction of the number of permitted duplications rapidly and correctly.
The present invention provides an information signal duplication control system comprising an information signal output device for outputting combined information signals generated by superimposing at least anti-duplication control signals on the main information signal and an information signal recording device for recording the main information signal in a recording medium correspondingly to the anti-duplication control signal in the combined information signal, wherein the information signal output device is provided with a spread code generator for outputting selectively one of a prescribed plurality of different spectral spread codes corresponding to the anti-duplication control signal for controlling the recording of the main information signal in the recording medium, a spectral spread portion for spectrally spreading the additional information signal to generate a spectral spread code information signal using the spread code supplied form the spread code generator, and a superimposition portion for superimposing the spectral spread code information signal supplied from the spectral spread portion on the main information signal to generate the combined information signal and outputting it, and the information signal recording device is provided with a spread code detector for receiving the combined information signal and detecting the spectral spread code used for generating the spectral spread code information signal contained in the combined information signal, an inversion spectral spread portion for performing inversion spectral spread on the combined information signal using the spectral spread code supplied from the spread code detector to obtain the additional information signal, an anti-duplication control signal generator for generating an anti-duplication control signal corresponding to the spectral spread code detected by the spread code recorder, and a recorder for recording the main information signal in a recording medium correspondingly to the anti-duplication control signal.